Recently, a technology to prevent resource depletion and global warming has been required. In particular, in the electric power field, renewable energy has been developed without resorting to fossil resource. By such renewable energy, the emission of carbon dioxide, which is one of heat-trapping gases, can be reduced. Renewable energy, such as sunlight, solar heat, water power, wind power, geothermal energy and biomass, can be obtained from a renewable energy source, which is supplemented from nature steadily and recurrently. For example, hydrogen is produced from biomass and electric power is generated from the hydrogen and air using a fuel cell.
In water electrolysis field, steam electrolysis has attracted a great interest in the last few years. When H2O is subjected to electrolysis to produce hydrogen and oxygen by steam electrolysis, gaseous water vapor is used without using liquid water. Steam electrolysis has the potential to be higher efficiency compared to conventional low temperature electrolysis, since operation under high temperature is possible and a portion of the required energy can be supplied as thermal energy.
Conventionally, an oxygen ion conducting electrolyte has been exclusively used in steam electrolysis. For example, Patent Document 1 discloses a steam electrolysis technology in which yttria stabilized zirconia having an oxygen ion conductivity is used.
However, when steam electrolysis using an oxygen ion conducting solid electrolyte is performed, electrode reactions occurring at anode and cathode are represented as follows.Anode: 2O2−→O2+4e−Cathode: 2H2O+4e−→2H2+2O2−
As the above formulae, in the above-described case, there is a problem that the step of separating the coexisting water vapor is additionally required, since hydrogen is generated at the cathode side.
In order to solve the problem, for example, the technology for steam electrolysis using a proton conducting electrolyte has been developed as described in Patent Document 2. In the invention, electrode reactions occurring at anode and cathode are represented as follows.Anode: 2H2O→O2+4H++4e−Cathode: 4H++4e−→2H2 
As the above formulae, in the above-described case, although hydrogen is generated at the cathode side similarly to the case of using an oxygen ion conducting electrolyte, the technology offers the advantage that it is not needed to separate hydrogen from water vapor, since water vapor is supplied to the anode side.
A perovskite oxide containing a transition metal in B site is used for an anode material of the steam electrolytic cell described in Patent Document 2, and the transition metal is exemplified by Co. In addition, Patent Document 3 discloses a perovskite oxide containing Ba and Co as a cathode material.